Meaning of "the" in Essential English Dictionary

the

determiner uk weak /ðə, ði/ uk strong /ðiː/

A1 used before nouns to mean things or people that have already been talked about or are already known:

Can you pass the salt?
I’ll pick you up at the station.

A1 used before nouns when only one of something exists:

the Eiffel Tower
the world

used before some adjectives to make them into nouns:

a home for the elderly

used before numbers that refer to dates:

Thursday the 29th of April

(Definition of “the” from the Cambridge Essential Dictionary © Cambridge University Press)